Lithium super-battery with a chemically functionalized disordered carbon cathode

Abstract

An electrochemical energy storage device, lithium super-battery, comprising a positive electrode, a negative electrode, a porous separator disposed between the two electrodes, and a lithium-containing electrolyte in physical contact with the two electrodes, wherein the positive electrode comprises a disordered carbon material having a functional group that reversibly reacts with a lithium atom or ion. The disordered carbon material is selected from a soft carbon, hard carbon, polymeric carbon or carbonized resin, meso-phase carbon, coke, carbonized pitch, carbon black, activated carbon, or partially graphitized carbon. In a preferred embodiment, a lithium super-battery having a functionalized disordered carbon cathode and a Li4Ti5O12 anode exhibits a gravimetric energy ˜5-10 times higher than those of conventional supercapacitors and a power density ˜10-30 times higher than those of conventional lithium-ion batteries. This device has the best properties of both the lithium ion battery and the supercapacitor.

Description

[0001]This invention is based on the research results of a project sponsored by the US Department of Commerce NIST Technology Innovation Program (TIP).FIELD OF THE INVENTION[0002]The present invention relates generally to the field of electrochemical energy storage device and more particularly to a new lithium-exchanging battery device featuring a cathode formed of functionalized disordered carbon and an anode containing a lithiated compound or lithium-containing material. This device has the high energy density of a lithium-ion battery and the high power density of a supercapacitor and, hence, is herein referred to as a lithium super-battery.BACKGROUND OF THE INVENTION[0003]Supercapacitors are being considered for electric vehicle (EV), renewable energy storage, and modern grid applications. The high volumetric capacitance density of a supercapacitor (10 to 100 times greater than those of electrolytic capacitors) derives from using porous electrodes to create a large surface area c...

AI Technical Summary

Problems solved by technology

Despite the positive attributes of supercapacitors, there are several technological barriers to widespread implementation of supercapacitors for various industrial applications.

On the other hand, lithium-ion batteries possess a much higher energy density (100-180 Wh / kg), but deliver a very low power density (100-500 W / Kg), requiring typically hours for re-charge.

Conventional lithium-ion batteries also pose some safety concern.

This intercalation or diffusion process requires a long time to accomplish because solid-state diffusion (or diffusion inside a solid) is difficult and slow.

Unfortunately, these organic materials exhibit very poor electronic conductivity and, hence, electrons could not be quickly collected or could not be collected at all.

Although these organic molecules contain carbonyl groups (>C═O) that presumably could readily react with lithium ions (forming a redox pair), this redox mechanism was overwhelmed by the poor electronic conductivity.

As a result, the battery cells featuring these organic molecules exhibit poor power densities.

However, the CNT-based approach still suffers from several relatively insurmountable technical and economical issues, which call into question the commercial viability or utility value of this approach.

Some of these issues are:(1) CNTs are known to be extremely expensive due to the low yield, low production rate, and low purification rate commonly associated with the current CNT preparation processes.

The high material costs have significantly hindered the widespread application of CNTs.(2) CNTs tend to form a tangled mess resembling a hairball, which is difficult to work with (e.g., difficult to disperse in a liquid solvent or resin matrix).(3) The so-called “layer-by-layer” approach (LBL) used by Lee, et al is a slow and expensive process that is not amenable to large-scale fabrication of battery electrodes, or mass production of electrodes with an adequate thickness (100-300 μm thick).(4) The CNT electrodes prepared by the LBL process have their thicknesses in the range of 0.3-3.0 μm.

Unfortunately, the data provided by Lee, et al (e.g. FIG.

A useful battery or supercapacitor electrode thickness is typically in the range of 50-500 μm (more typically 100-300 μm).(5) Although the ultra-thin LBL CNT electrodes provide a high power density (since Li ions only have to travel an extremely short distance), there was no data to prove that CNT-based electrodes of practical thickness could even work due to the poor dispersion and electrolyte inaccesability issues.

Lee, et al showed that the CNT-based composite electrodes prepared without using the LBL approach did not exhibit particularly good performance.(6) CNTs have very limited amount of suitable sites to accept a functional group without damaging the basal plane or graphene plane structure.

By chemically functionalizing the exterior basal plane, one would dramatically compromise the electronic conductivity of a CNT.

This insertion or extraction procedure is slow.

Due to this slow process of lithium diffusion in and out of these intercalation compounds (a solid-state diffusion process), the conventional lithium ion batteries do not exhibit a high power density and the batteries require a long re-charge time.

None of these conventional devices rely on select functional groups (e.g. attached at the edge or basal plane surfaces of a graphite crystal in a non-crystalline carbon matrix) that readily and reversibly form a redox reaction with a lithium ion from a lithium-containing electrolyte.

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